Fiber composite and process of manufacture

ABSTRACT

The inventive fiber manufacturing process is particularly adapted for demanding applications such as sports racquets, including tennis racquets, badminton racquets and other sports applications. Because of the improved strength to weight ratio of components formed using the inventive method, a wide range of flexibility is achieved, allowing use of the inventive process to manufacture, for example, a fiber reinforced (for example, graphite) modular sports racquet, optionally provided with user-selectable weights and/or handle replacements. From the standpoint of the player, this allows a racquet frame featuring self customization. From the standpoint of a retailer, the benefit provided is reduction of inventory. The inventive fiber, for example graphite fiber) racquet frame is filled with a plastic foam and is formed using, for example, microencapsulation technology to time, generate and apply the pressure used to form the graphite composite material of which the racquet is comprised. Advantageously, inner and outer tubular members may be used to form the racquet frame, with the inner tubular member extending around the head of the racquet frame. This compares to the standard industry technique of air injection. The racquet is thus not hollow like conventional graphite racquets, and the walls therefore can be made thinner than those of existing graphite racquets still being of the same strength or being stronger, which gives the racquet exceptional performance. In addition, the overall dimensions of, for example the cross-section, of the racquet can also be reduced while still maintaining performance characteristics.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of PCT application No.PCT/2010/038664, which in turn claims priority of Chinese patentapplication number 200910040320.9, filed on Jun. 18, 2009 in thePeople's Republic of China, and the priority of U.S. Provisional PatentApplication No. 61-285,051, filed on Dec. 9, 2009, the disclosures ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to apparatus and methods for graphite resincomposite members, such as sports racquet frames, golf club shafts andbicycle frames.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

(Not applicable)

BACKGROUND OF THE INVENTION

For many years, graphite composite sports racquet frames have beenproduced by manual labor in molds using air injection. In a typicalprocess, a “layup” is created by manually rolling multiple sheets orlaminations (which take the form of strips of planar material), commonlyformed of fibrous material, such as carbon or graphite fiber orfiberglass, to form a bladder. The bladder is formed, for example, usinga number of “sheets” of graphite fiber, permeated, for examplesaturated, with an uncured thermoplastic or thermosetting resin.Generally, the sheets are wrapped by hand around a rigid mandrel or rodto control the desired layup shape, which is usually in the shape of atube.

Before the graphite is wound on the mandrel, the mandrel is wrapped witha layer of material meant to form the internal surface of a layupbladder to be inflated during the manufacturing process as set forthbelow. The sheets are made of carbon fibers and, as alluded to above,permeated with an uncured plastic resin. These carbon fiber/resin sheetsare manually cut into strips or ribbons prior to their assembly into alayup, typically by being wound around a mandrel to form a tube. Afterbeing wound, the layup (which, after winding, takes the form of abladder) is manually formed into a desired racquet shape, reinforcedwith additional patches of the planar strips of carbon fiber permeatedwith resinous material, and placed in a mold. By resinous material ismeant any material which can be used in graphite or fiberglass compositeto bind the fibers into a substantially rigid structure.

The mold is then manually closed. The bladder is subjected to heat bythe mold, causing the thermoplastic resin to cure. The result in thefinished racquet is a hardening of the material of the layup.Alternatively, thermosetting resins may be used.

The bladder is then inflated with a manually placed single air nozzle,which is individually attached to one end of the bladder. The nozzlefeeds, for example, air pump generated compressed air to force the wallsof the layup to the interior walls of the mold cavity. See Hsu, U.S.Pat. No. 4,511,523 (1985). Because both ends of the layup are formedwith an open configuration, the terminal end of the layup opposite theend being inflated by the nozzle is coupled, for example, to a cappingor other sealing structure or artifice, allowing the buildup of pressurein the layup. The mold is then heated to cure the thermoplastic resin.

An artifact of this process is that composite racquet frames arecommonly of a single-tube design. The two ends of the layup tube may be,for example in the case of tennis racquets, at the bottom of theracquet. In other words, the tube begins at the base of the tennisracquet handle, proceeds in a substantially straight direction along thelength of the tennis racquet handle, extends around the oval stringsupporting frame shape and continues contiguous with the initial portionof the tube in a substantially straight direction back to the base ofthe tennis racquet handle. Typically, the base of the handle is cut atits end with a saw and a pair of gripping members secured around thoseportions of the tube ends which define the tennis racquet handle.Because of the requirement of air injection, the tubular basic shape isrequired to blow air through the entire tube which means the immediateoutput product is hollow with the above technique and necessarily has anopen ended shaft at the bottom or base of the tennis racquet handle.

While it may be possible, in principle to the form a multiple-tubecomposite structure, it has been found that any internal divisions,bridges or lumens placed in these tubes are difficult to control intheir placement because of variations in bladder air pressure and layupcharacteristics along the length of the layup. Attempts to include themin the past have been found to cause significant quality control andproduction problems.

On the one hand, due to the hollow nature of graphite racquets, aminimum cross-sectional width is required in, for example, the hoop orhead portion of the tennis racquet in order to enable the tennis racquetto be strong enough to withstand the powerful strokes typical of thegame. For example, professional tennis players can achieve ball speedsof 150 mph during a serve.

On the other hand, thinner frames are desirable because of the increasein swing speed, head speed, control and feel. The quality of thematerial which forms the racquet frame manufactured using the currentstate-of-the-art the air pressure process is such that the resultinghollow frame is limited to a minimum width, typically about 19 mm.

SUMMARY OF THE INVENTION

Quite apart from the strength of the material of which the tennisracquet is made, in accordance with the invention it is also believedthat the hollow nature of present state-of-the-art graphite racquets, incomparison to earlier generation solid wooden racquets, have increasedinjury to shoulders and elbows due to vibration and shock, particularlyfrom off-center shots. This is because the hollow frame and open endedshaft at the handle is coupled, during play, to the hand and then to thearm.

In accordance with the invention, the opening for air injection at thebottom of the shaft is believed to worsen the shock that resonates atthe handle of the racquet and propagates to and through the hand, armand shoulder of the player.

Years of industry development have been invested to address theminimization of these propagated vibrations and shock, by implementingvarious methods of dampening the transmission of vibration from thehandle of the racquet to the hand of the player.

The invention addresses these issues by providing a carbon compositeframe structure of increased strength and reliability, providing theframe head and handle with an inner core of foam plastic and,optionally, providing for a truly closed end at the base of the racquethandle.

In accordance with the invention, it is believed that closing the endsof the racquet may further improve this aspect of the performance of asports racquet.

Solid wooden racquets, compared to graphite racquets, absorb the shockand as a result, the prior generation of wooden racquets did not producethe number of shoulder and elbow injuries associated with hollowgraphite racquets. In accordance with the invention, it is believed thatthe air injected graphite era of racquet manufacturing has produced aconsiderably higher incidence of elbow and shoulder injuries, not onlydue to the hollow nature of conventional graphite racquet technology,but also because of the open ended shaft at the end of the handle.

Conventional hollow racquets are also particularly prone to propagatevibration and shock associated with off-center shots because the energyfrom the “mishit” feeds into the hollow frame. The inventive solid frameon the other hand reduces this shock and increases the size of the“sweet spot” on the frame because the energy of the off center shot doesnot propagate well, into or through the inventive frame. In accordancewith the invention, the combination of a thinner and solid racquet alsocreates a larger “sweet spot” because it diminishes the propagation ofshock. The result is surprisingly increased “forgiveness” for off-centershots.

The implementation of a sports racquet with a foam core is not unknown.U.S. Pat. No. 4,129,634 to Cecka (1978) discloses the use of a foamplastic material to form an internal filler member within the core ofthe head of a sports racquet. However, over the many years of graphiteracquet manufacture, such foam technology has not, to the knowledge ofthe inventor, seen substantial commercial implementation within thecritical structure surrounding the head of the racquet that supports thestrings.

In accordance with the invention, foam type materials are used topressurize and mold the graphite. However, the mere use of foam topressurize and mold the graphite is not sufficient. For example, thecuring temperature of carbon resin is typically in the range of 130degrees Celsius. The foaming agent must be of a type which substantiallydoes not expand before the temperature needed to cure, for example, upto six layers of carbon fibers, is reached. Likewise, it is believedthat expansion must be relatively rapid, because slow expansion maycreate pitching of the fibers in the frame structure while it is curingin the mold.

A racquet might also fail to perform satisfactorily if the layerlamination pressure is not enough. Likewise, if the foaming materialdensity is too high, even though the expansion rate reaches the requiredlevel, it may not meet the lightweight target for a particular carbonfiber product. The expansion coefficient of the foam plastic formingmaterial used in accordance with the invention, Expancell 152 isbelieved to be about 60 to 1. Solid foam materials which have expansionratios in the range of about 2 to 1 have been found not to produceracquets of sufficient strength. Jellied type foam materials havingexpansion ratios in the range of about 10 to 1, while measurablyimproved, are also less than ideal. Surprisingly, micro encapsulatedfoaming plastic materials provide good strength in the finished productand excellent playing characteristics, probably due to a combination ofthe cellular plastic structure and the pressure applied.

Implementation of the invention may be varied depending upon therequirements of a particular application, some of which may tolerateweight (for example certain tennis racquets meant for players who prefera heavier racquet), and others of which may not require as muchstrength, but might benefit from cost savings associated with using lesscarbon fiber (for example badminton racquets, which are a much lesscritical application).

It has also been discovered in accordance with the invention that if theexpansion temperature is too high, it will cause difficulties inmolding. When the expansion rate is too low, this can adversely affectthe strength of the carbon fiber member because of pitching.

Thus, while the formation of a sports racquet frame using a foam plasticmaterial (to apply pressure to the carbon fiber and resin layup duringformation and after formation to reduce vibration), under a broad rangeof conditions employing a wide variety of materials, will result in aplayable racquet frame, a racquet with superior performance can beachieved if the above parameters are followed.

Nozzle applied air pressure has been industry practice in manufacturinggraphite racquets for the many years. Because the air nozzle must beattached manually, and because of the inconsistencies with which the airnozzle fits into the latter, the process cannot be efficientlymechanized.

The process of making the racquet in accordance with the invention usesa micro encapsulated plastic material, including a foaming agent in theform of a powdered material, to form the foam plastic. This material isput into the tubular layup bladder which is sealed at both ends. Thebladder is then put in an iron mold which is then heated. This resultsin the material being heated, causing it to melt and expand under thepressure of a foaming agent contained therein.

Because no nozzle injection of air is involved, the labor associatedwith making this connection is eliminated, and the manufacturing processis made substantially more uniform and less time-consuming. This aspectof the invention also presents the opportunity of mass-producing theracquet frame, for example in a completely automated process.

In accordance with the invention, it is noted that the foaming of theplastic which forms the foam plastic inner core of the racquet occurs ata temperature roughly about the temperature required for the curing andfusing of layers of the carbon fiber/thermoplastic resin sheets whichform the layup bladder, although somewhat higher temperatures can betolerated. The particular temperatures are a function of the materialbeing used to form the foam plastic and may be obtained by routine trialof the same and checking the final product to be verify that thetemperature has not been excessive.

In accordance with the invention, one fills the layup with the powdermicrocapsule foaming plastic material, which does not begin to expand,in the examples set forth below, until the temperature reaches 120-130degrees Centigrade, for example 130° C. At the same time, the gasgenerate pressure, inside the layup bladder which is sealed at bothends, due to the foaming action of the micro encapsulated materialinside the bladder. This makes the fiber layer laminations, which formthe racquet frame in the finished product, press up against the insidesurface of the mold to take the shape of the mold cavity.

It is understood that when heat is applied, the micro encapsulatedfoaming agent expands and deforms the capsules enclosing it, thusforming a foam plastic under pressure. This results in creating enoughpressure to press the layers of graphite carbon fiber against the moldwalls to form the carbon fiber into the shape of the cavity of the mold.The combination of heat and pressure results in fusing of the layers andthe formation of the composite material of which the racquet frame ismade. This occurs at the temperature of about 120-130 degrees Celsius.This temperature range may vary depending upon the characteristics ofthe thermoplastic material forming the carbon fiber sheet.

In accordance with a preferred embodiment, the temperature, at which themicro capsules expand and allow the foaming agent to form the foamplastic, is about 130-135° C., although suitable results can be achievedat temperatures well above that level. Likewise, if the thermoplasticresin in the sheets incorporating the carbon fibers have a sufficientlylow softening point, lower temperatures may be used.

The plastic foam created when the powder micro encapsulated foam plasticmaterial is heated, when cooled, will substantially hold its volume andnot shrink. After cooling, the plastic material thus solidifies in theshape of the inside of the mold cavity.

It has been found that the inventive method of using a foam plasticmaterial, which, when heated, forms a foam plastic which is caused toexpand close to or above the temperature at which the plastic material,incorporated into the graphite fibers, cures and fuses, in addition toeliminating the need for handwork in the attachment of an air nozzle (aswell as the associated problems and irregularities associatedtherewith), also achieves a superior weight to strength ratio in thecomposite fiberglass material.

The inventive method thus allows the formation of a racquet frame withthe same strength as a wider (for example in cross-section) conventionalframe, and at the same time eliminates the problems associated withmanufacturing methods employing nozzle-supplied air pressure.

In accordance with the invention, it is noted that similar equivalenttechniques may be used. For example, a microencapsulated foaming agentmay be put in a frangible shell and mixed with powdered plastic whichwould melt before the microcapsules would break and release the foamingagent. Alternatively, the microcapsules may only melt at the desiredtemperature and fuse with particles of the plastic powder. By usingvarious combinations of plastic and microcapsules a variety of plasticcharacteristics can be achieved, including strength, flexibility,damping, weight rigidity, compressibility, density and so forth. Forexample, a rubbery material may be incorporated with microcapsulesfilled with pentane to increase shock and vibration absorption.Alternatively, a rubbery material may be used for the microcapsules.

Alternatively, the recipe may also include elongated plastic particleswhich are selected for rigidity and which may also have characteristicswhich result in their not melting during the generation of pressureduring the foaming process for the purpose of fusing multiple layers ofcarbon fiber. A rubbery material optionally included in the recipe wouldresult in shock and vibration absorption, while a desired rigidity wouldbe provided by the elongated plastic particles.

Still another possibility is the incorporation of elongated particleswhich may be oriented. For example, elongated electret particles, whichwill not melt or lose their polarity at the temperatures needed forgraphite racquet formation, may be introduced into the mixture ofmicrocapsules and oriented by electric fields while still in the moltenconfiguration, thus resulting in orientations which could addressparticular needs in terms of strength, damping, and so forth. Forexample, this technique may be used to form a bicycle frame in whichdifferent orientations of particle electrets are achieved by applyingelectrical fields of corresponding orientation to different parts of theframe to address the stresses formed at those parts of the frame duringuse.

Conventional tennis racquets also come in a variety of grip sizes, gripshapes, weight, balance and swing weight configurations. Racquets withdifferent configurations are typically done at the manufacturer levelbecause modifications in the field or by consumers are difficult. Theresult is that stores are compelled to carry large inventories ofvarious types of tennis racquets. This also means that the distributionsystem is inefficient and results in extra costs in the supply chain.The modular aspect of the inventive racquet allows it to be easilycustomizable into various configurations which address this deficiencyof current products.

The inventive resin and fiber composite may comprise an outer shelldefining a cavity, the outer shell comprising a plurality of layers offibers. A first resinous material is disposed between the fibers andsecures the fibers to each other. A second resinous material is disposedinside the cavity, the second resinous material being configured anddimensioned to define voids within the cavity between portions of thesecond resinous material. A gaseous material is contained within thevoids, the gaseous material being under a pressure in excess of 20 psi,but more preferably 30 pounds per square inch, and most preferably inexcess of 40 psi.

A foaming agent is disposed in the cavity. The foaming agent and thesecond resinous material are adapted to interact during curing to createa resinous structure configured and dimensioned to define the voidswithin the cavity between portions of the second resinous material.

An inventive resin and fiber layup, comprises a plurality of layers offibers configured as a closed bladder which defines an internal cavitywithin the bladder. A quantity of a first resinous material is disposedbetween the fibers and is adapted to be cured to secure the fibers toeach other. A second resinous material disposed inside the cavity. Afoaming agent is disposed in the cavity. The foaming agent and thesecond resinous material are adapted to interact during curing to createa resinous structure configured and dimensioned to define voids withinthe cavity between portions of the second resinous material. The voidsmay be closed or open cell voids.

The fibers may be in layers with different orientations. A layer of anair impermeable of material may be disposed in the cavity positionedbetween the second resinous material and the plurality of layers offibers.

The cavity may be a closed cavity. The gaseous material may be under apressure in excess of 5 kg/cm², for example in excess of 20 pounds persquare inch, preferably more than 30 psi, and upon information andbelief most preferably greater, perhaps in excess of 40 or 50 psi, or aslarge as the pressure created in the embodiments described below inconnection with a tennis racket main frame layup provided with 25 gramsof Expancell 152. For many applications pressures in the range of 5-15kg/cm² will yield excellent results.

One or both end portions of the sleeve on which the layup is wrapped maybe configured as a knot or a fold.

The resinous material disposed between the fibers may be adapted to becured by heat. The second resinous material may be adapted to be curedby heat. The second resinous material may encapsulate the foaming agent.

The second resinous material encapsulates the foaming agent and iscaused to expand at about same temperature as the curing temperature forthe first resinous material.

The second resinous material and the foaming agent may not be rigid inform and may be in a powdered form.

The second resinous material and the foaming agent may have an expansionratio greater than 30, or preferably in the range of about 50-70, forexample 60.

The inventive method of making a fiber composite member, comprisesforming flat members of fiber permeated with resinous material, andwrapping the flat members around a mandrel. A foam plastic formingmaterial is placed within the wrapped flat members. One thensubstantially closes the ends of the wrapped flat members to define asubstantially closed bladder. One then introduces the closed bladderinto a mold, causing the foam plastic forming material to form a foamplastic. the resinous material is then cured, for example by heat.

The cured layup is removed from the mold. Alternatively, the mold is amember which forms a permanent part of the fiber composite member.

Preferably, one covers the mandrel with a sleeve prior to wrapping thefiber layers. An adhesive material may be used to tightly secure thesleeve around the mandrel. The mandrel may be a two-part mandrel.

The fiber may be graphite fiber. The foam plastic forming material mayform foam plastic when subjected to a temperature close enough to thetemperature at which the resinous material cures under the applicationof heat so that the foam plastic exerts pressure on the layers of fiberwhile the resinous material is curing.

Advantageously, inner and outer tubular members may be used to form theracquet frame, with the inner tubular member extending around the headof the racquet frame.

Accordingly, it is an object of the present invention to provide amethod for producing a racquet frame made from composite material, inwhich gas injection is not needed to expand the composite material toform the racquet frame and the frame can be completely enclosed duringthe manufacturing process in a closed mold.

It is another object of the present invention to provide a method forproducing a racquet frame which, while being at the low end of the rangeof acceptable racquet weights, still has the strength necessary to playwell under demanding conditions of play. This means that a singleinventive racquet may be modified through substantially the full rangeof player weight preferences and distributions. In accordance with theinvention, this can be achieved, after manufacture of the frame, andeven after stringing of the frame, by installing objects which may bemounted to the frame and even incorporating weights inside the frame.

It is also possible to incorporate weights at various positions on theframe. These positions may be selected in order to optimize racquetcharacteristics during play. This compares to conventional racquets,where the weight of the graphite/polymer composite was often neededaround the circumference of the head in order to support the strings.Moreover, structures incorporating weights, if they had beencontemplated, would have presented complications in conventionalmanufacturing processes, insofar as there was an increased likelihoodthat an air passage might be blocked during manufacture in aconventional airflow manufacturing method.

It is another object of the present invention to provide a very thinsolid racquet frame which reduces shock over and above a conventionalhollow frame and increases performance due to swing speed and headspeed, and by virtue of having a larger hitting zone or “sweet spot”.

It is another object of the present invention to provide a modularracquet fully customizable in the field by ordinary consumers.

This method can greatly enhance graphite rigidity and strength to formmore powerful strokes and shots in sports. It can also be expected todecrease the shock and vibration associated with tennis elbow andshoulder injury by creating a closed solid filled product. In accordancewith the invention, such a structure is achieved because the oppositeends of the tube are closed and the entire tube is optionally put in amold which is completely closed. This is in contrast to prior artmanufacturing methods which include a nozzle and a cap which protrudeout of the mold, and result in additional hand labor to fit the nozzleand the cap, prior to curing of the resin and sawing of the base of theframe handle after the resin has cured and solidified.

It is another object of this invention to provide a method of shapinggraphite fiber members, and a manufacturing operation, including asingle curing step, for manufacturing graphite fiber elements intovarious shapes otherwise not attainable with conventional air pressuremolding. More particularly, this may be achieved because the shape ofthe part being manufactured need not provide for a continuous path forairflow. Instead, a number of platters may be assembled, and theassembled bladders then put together in a desired configuration forheating and curing.

It is another object of the invention to provide a method formanufacturing a graphite fiber composite member without an inner nylonbladder, relying upon the viscosity of the foaming plastic to preventair leaks through a carbon fiber/resin layup.

It is another object of this invention to provide a method which solvesthe problem of inconsistent racquet characteristics due to theirregularities and other problems associated with the nozzle airinjection process.

It is another object of this invention to manufacture graphite racquetsby use of machines and to minimize or eliminate human labor.

Another object of the invention is to provide a framework for theproduction of a composite fiber resin racquet, which can be easilyloaded with weights to adjust the racquet's weight and balance.

Another object of the present invention is to mold a racquet frame withholes, thus eliminating the need for drilling holes after manufacture ofthe frame. This may be done by assembling two half-racquet layups,placing one of the half-racquet layups in the bottom half of the mold,placing a plurality of pins, positioned where the holes belong, in slotsprovided in the mold, and then placing the other half-racquet layup overthe first half-racquet layup and closing the mold using the other halfof the mold.

In one embodiment of the invention, the racquet also uses a closedracquet handle base formation with the object of reducing injuries fromshock and vibration, as compared to racquets with the open ended shaftof present state-of-the-art graphite racquets.

BRIEF DESCRIPTION THE DRAWINGS

The operation of the invention will become apparent from the followingdescription taken in conjunction with the drawings, in which:

FIG. 1 shows a prior art graphite tennis racquet;

FIG. 2 illustrates a cross-section of tennis racquet using a rigidunencapsulated foaming plastic as described by Cecka, U.S. Pat. No.4,129,634 in a prior attempt at using foaming agents to manufacture acarbon-graphite racquet;

FIGS. 3-5 illustrate the prevailing industry practice using airinjection to form the main portion of a graphite racquet frame, asdescribed by Hsu, U.S. Pat. No. 4,511,523 forming graphite racquets;

FIG. 6-7 illustrates the construction of a layup useful in the practiceof the inventive technology;

FIGS. 8 and 9 illustrate the curing of a tennis racquet using a foamplastic generating composition comprising microcapsules incorporatingfoaming agent sold under the trademark EXPAN-CELL 152 used in accordancewith the invention;

FIG. 6 is a perspective view of a closed cellophone tube containing themicrocapsulated foaming agent which can be made by machine;

FIG. 7 is a closed tubular shell formed from a cellophane tubecontaining the microencapsulated foaming agent in cell 152, with thetube wrapped with a closed multi-ply sheet of resin impregnated fiberforming a tube in accordance to with the present invention which may beformed by machine rather than human labor.

FIG. 8 is the fiber tube shaped for the formation of the racquet whichcan be placed in a mold by machine;

FIGS. 9 a and 9 b are horizontal cross-sections through the frame headof FIG. 8 showing the Expancell 152 inside the fiber tube comparing thepre thermoform (that is prior to the application of heat and thephysical softening and expansion of the microencapsulated foaming agent)FIG. 9 a and the post thermoform state (that is subsequent to theapplication of heat sufficient to cause the microcapsules to expand,under the action of the foaming agent and cause the foam to expand andforce the carbon fiber to the inner walls of the mold forming theracquet) FIG. 9 b;

FIG. 10 is a cross sectional view of another embodiment of the inventionwhereby post-thermoformed microencapsulated graphite tubes are placedwithin fiber tubes for the formation of tubes within tubes;

FIG. 11 is the cross section of another embodiment of the presentinvention, showing two tubes which have been formed prior to beingwrapped with a second tube to form the string supporting hoop or headportion of a tennis racquet;

FIG. 12 a illustrates molding of the handle portion of a racquet;

FIG. 12 b is a cross section view of a tube within a tube structure;

FIG. 13 illustrates making a frame head;

FIG. 14 illustrates the construction of a badminton racquet;

FIGS. 15 and 16 show yet another embodiment of the invention withracquet weight distribution;

FIG. 17 shows a finished customizable racquet 14 in exploded plan view;

FIGS. 18-25 illustrate the making of carbon fiber patches for use inmaking the inventive frame and practicing the inventive method;

FIGS. 26-27 shows the makup of a graphite assembly used to begin thewraping of a layup for a badminton racquet;

FIG. 28 shows a two-part mandrel for wraping the inventive layup;

FIGS. 29-36 illustrate wrapping of the inventive badminton racquet;

FIG. 37 illustrates a tool for filling a layup with microcapsules;

FIG. 38 illustrates a wood mold for forming a badminton racquet head;

FIGS. 39-49 illustrate further wrapping of the inventive badmintonracquet;

FIG. 50 illustrates a mold for curing of the inventive badmintonracquet;

FIG. 51 illustrates the parts of the inventive tennis racquet;

FIGS. 52-54 illustrate the formation of a layup for the inventive tennisracquet;

FIGS. 55-56 illustrates alternative heat-curing molds for the formationof handles for the inventive tennis racquet;

FIGS. 57-60 illustrate completion of the formation of a layup for theinventive tennis racquet;

FIG. 61 illustrates a heat-curing mold for completion of the formationof the inventive tennis racquet;

FIG. 62 illustrates diagrammatically a layup for an alternativeinventive tennis racquet; and

FIG. 63 illustrates diagrammatically the molding and heat-curing of thealternative tennis racquet of FIG. 62.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a conventional graphite racquet frame 11 in the prevailingand desired racquet shape. When fabricated using air injection graphitemanufacturing techniques, it has an advantage in strength to weightratio over the predecessor wooden racquet. The racquet frame 11 has ahead portion 12, a throat portion 13, a handle or shaft portion 14, andgrips 15 which overlie handle 14. These portions of racquet frame 11 areformed as a single, integral and continuous member. Bifurcated throatportion 13 is continuous with the head portion 12 and with shaft portion14. A crosspiece or yoke portion 16 is provided between both sides ofthroat portion 13. Yoke portion 16 and head portion 12 form a roughlyoval string-stretching portion 17 surrounding a ball-hitting face 18. Astring groove 19 is concavely formed on the outer surface of the headportion 12.

FIG. 2 illustrates a prior art tennis racquet frame structure asdescribed in U.S. Pat. No. 4,129,634 to Cecka. Here, frame 11′ includesan outer surface formed by layers of graphite fiber 20 and an inner foamcore 22. This product is made by rolling multiple layers of carbon fiberover a central putty like core. The core principally comprises fillermaterial, such as cork, resin (such as a thermosetting resin), andblowing agents to achieve foaming of the resin, as well as anaccelerator and curing agent. During manufacture, the racquet layup isput in a tool steel mold and heated. The pressure generated by theblowing agent during the formation of the foam core is intended toprovide pressure which conforms the outside shape of the layup, aftercooling, to the shape of the mold. As alluded to above, this technologyis not believed to have been commercially employed, perhaps on accountof the unfavorable racquet characteristics, as the simple inclusion of afoam plastic core does not, of itself, result in improved playingcharacteristics as has been discovered in accordance with the invention.

In accordance with the invention, expansion of the foam plastic is timedto substantially coincide with or follow the softening of the plasticwhich forms the foam core of the inventive racquet. Prior to curing, theresin which saturates the graphite fibers is a sticky soft material.Accordingly, if expansion is not carefully timed, it is possible for thesame to occur somewhat prior to curing and then for curing to occur,perhaps after pressure has been lost.

In accordance with the invention, the foam core may comprise an opencell or closed cell foam plastic. The material used in the preferredembodiment, Expancell® has the advantage of being somewhat liquid duringformation of the foam plastic. It is also believed that closed cell foammay provide an advantage in ensuring that in the event of a leak theclosed cell material may be more effective in quickly filling the leakand because of its viscosity compared to air more effective inpreventing air escaping and thus pressure loss.

The curing temperature of carbon resin may be, for example, 130 degreesCelsius. The internal pressure used at 130 degrees Celsius to press thecarbon layer against the mold and to adhere the sheet carbon fiber resinlayers together before resin is cured should at least be from roughlyaround 7 kilograms/cm² (about 100 psi) to 15 kilograms/cm² (or about 215psi), although 5 kg/cm² is sometimes employed in some applications. Thefoaming plastic to be selected is preferably able to reach this pressureduring curing. This can most easily be achieved when foaming beginsafter the resin is at its curing temperature and may be cooled beforethe pressure is lost.

Moreover, many foams can only expand to 2-3 times in size and because oftheir size would cause the fiber to be clipped outside the desired moldshape. The clipping of the graphite fiber yarn would damage theconstruction and jeopardize the construction and strength.

It is noted that if expansion does not occur at the proper time, theracquet will still look like it is properly made. Adhesion betweengraphite layers and between the foam core and the graphite layer mightalso be good. However, adhesion between the graphite layers might not begood enough to result in excellent and/or long-term performance by theracquet frame. Thus, it is important that sufficiently high pressure beapplied by the foam after the resin has been polymerized and is ready tobe cooled. Of course, it is possible for such pressure to be createdprior to polymerization, provided that the same is at a high enoughlevel when polymerization occurs.

It appears that if loss of pressure after polymerization occurs, this isnot critical because pressure has been applied to the graphite layerscausing them to be securely bonded to each other, and loss of pressure,even while a thermoplastic frame is in the softened state may not affectframe characteristics in the cooled product.

It is further noted that the use of a powder foaming plastic material,for example an encapsulated foam, allows the layup to be pressed flat toprevent the clipping of the graphite in the mold when the mold is closedbefore the resin saturating the carbon fiber is heated and cured.Expansion which is too slow can also create pitching of the fibers bythe mold outside the mold cavity.

Using foam type materials to pressurize and mold the graphite can failbecause the layer lamination pressure is not high enough and because ofthe low carbon fiber expansion rate. If the foaming material density istoo high, even though the expansion rate reaches the required level, itwill not be as lightweight as is desired for carbon fiber reinforcedproducts.

FIGS. 3-5 show the prevailing air pressure racquet making technologyused today. The carbon fiber used to make the layup takes the form of agraphite sheet. Graphite sheets are wrapped around a seamless sleeve toproduce the layup.

Air pressure is forced through an inflation assembly 31, comprising avalve 30 coupled by nozzle 32 for receiving a source of air pressure, asshown in FIG. 3. Inflation assembly 31 is coupled at one end to a sourceof compressed air and to the sleeveless tube of the layup 33 at theother end. Layup 33, formed of an inner tubular member and layers ofgraphite material impregnated with resin, is placed in the cavity 59defined by mold halves 61 and 62 of mold 60 for heating and curing ofthe layup, under the application of air pressure, in order ultimately toform the molded and cured frame. See FIG. 4.

The prefabricated soft carbon tube layup 33, formed of carbon fiber anduncured resin, is placed into cavity 59 defined between steel moldhalves 61 and 62 of mold 60 when the clamshell is closed. Air nozzle 31is coupled by its female nozzle coupling 32 to a source of compressedair, which may be sealed by a mating male nozzle.

The finished layup is placed in a bottom mold section 61 and thencovered by the upper mold section 62. See FIG. 5.

The nozzle is attached to one end of the seamless sleeve to create thenecessary air pressure inside the sleeve to form the carbon to the moldcavity 59 at the curing temperature, which is typically around 130degrees Celsius. The other end of the seamless sleeve may be sealed, orone may rely on air rushing through one end while it is in the mold toblow up and seal the opposite end of the seamless sleeve by bringing thetwo ends of the sleeve together in a single tubular portion of the mold.

After the graphite composite has been cured, it is allowed to cool.Next, finishing of the racquet including removal of excess material,sanding and removal of the base of the handle or shaft of the racquet,for example by sawing, is performed.

From this it will be understood that the bottom of the shaft is open andhollow. Moreover, in order to implement conventional manufacturingmethods, this is necessary in order for air to be injected into thecarbon tube while heated. The resulting racquet will accordingly have anopen ended shaft as a result of this process.

In the preferred embodiment, a material understood to comprise plastichollow microspheres is used to form the foam plastic. The microspheresare spherically formed particles with a thermoplastic shellencapsulating a gas. When the microspheres are heated the thermoplasticshell softens and the gas increases its pressure, resulting in anexpansion of the spheres. The microspheres or microcapsules includingthe foaming agent are about 10-30 microns in diameter, with a thicknessof 5-15 microns and density of 1.03 g per cubic centimeter.

In accordance with the preferred embodiment, curing temperature for theresin is about 140-150 degrees Centigrade. The racquet frame or othercomposite part should be held at this temperature for about 20 to 35minutes.

The expansion ratio of the foam plastic foaming material selected inaccordance with the invention (Expancel 152) is believed to be aboutsixty to one. In accordance with the invention, microcapsule foamforming material used starts to expand from around 105-115 degreesCentigrade and higher. It can continue to expand significantly until thetemperature drops to under around 105 degrees Centigrade. However, theabove temperature may vary depending on the particular foaming plasticproduct used. Significant factors in this may be the resin used, thefoaming agent, and the nature of the microcapsule.

Thus, the microcapsules substantially do not begin to expand until thetemperature is close to the temperature needed to cure and fuse thegraphite fiber composite material. The shell of the capsule isunderstood to be made of an acrylic copolymer resin. The shell material,after expansion, can form the material of the final foam core of thegraphite racquet. Alternatively, additional materials, such as graphitewhiskers may be incorporated in powder form and mixed with themicrocapsule powder to achieve different characteristics. The foamingagent may be pentane or any other foaming agent suitable for thematerial of which the microcapsule is made and for the application, forexample tennis racquet frames.

In accordance with the invention, the particular foam plastic materialwhich is deposited in the layup is Expancel 152, available commerciallyfrom Akzo Noble. A predetermined quantity of the Expancel 152 is placedinto the seamless tube and the layup is rolled to more evenly distributethat material.

Opposite ends of the filled layup are sealed, for example by tying theends of the seamless tube on which the resin-impregnated carbon fiberstrips are wrapped. The filled layup is then formed roughly in the shapeof the product being made, for example a tennis racquet, and placed inthe mold cavity in the bottom of the mold. The top of the mold has asimilar or substantially identical cavity, and the layup is carefullyfitted to be contained in the cavity, and to avoid pinching of the layupby surfaces of the mold adjacent to cavity.

The mold is then heated. Once the desired temperature is reached, asunderstood, the microcapsules will soften and the foaming agentassociated with the Expancel 152 expands in size. When cooled, theexpanded microcapsules, which now form a foam plastic core, willsubstantially hold their volume.

Thus, in accordance with the invention, it is simply necessary to putpowdered polymeric beads containing the foaming agent in the layup andfollow the process steps of sealing the layup, putting the layup in themold and heating to the desired temperature.

It is also noted that the invention will work with microspheres whichmaintain their physical sealed characteristic after heating, as well asmicrospheres which open, fracture or physically break down ordeteriorate when they are heated.

In principle, it may be possible to add other polymeric materials, forexample, fine plastic powder, or other suitable material, to theExpancell 152 to vary the characteristics of the foam filling the insideof the finished racquet.

This can be seen more clearly with reference to FIG. 6, where a tubularseamless sleeve 40, covered with carbon fiber layers 42 and 44, filledwith microcapsules 21 of EXPAN-CELL-152 is illustrated. Sleeve 40 isclosed, for example, by knotting the ends of the seamless sleeve closed,or as an alternative this may be achieved using a machine process, suchas the application of staples or clamps, or by heat sealing, as opposedto using hand labor.

FIG. 7 shows, in schematic form, the soft, for example graphite, fiberwrap to make the fiber wrapped layup tube 33. It is formed from anopen-ended, for example clear, tubular seamless sleeve shell 40 wrappedwith a multi-ply sheet of a resin impregnated carbon fibers. Inprinciple, fiberglass or graphite fibers permeated with the resin may beused. The layers, for example six different layers of fiber 21-27, canbe of different fibers (or the same fiber). For example, layers 22, 24,and 26 may have different characteristics and/or different resins,and/or different orientations. These layers form the soft unheatedcarbon tube layup 33.

As shown in FIG. 8, the closed finished soft fiber tubular layup 33,containing microcapsules in core sleeve 40, is fitted into the recess 43in bottom mold section 61. Core sleeve 40 is also sealed at both ends.Sleeve 40 is curved to the general shape of a racquet to be placed intorecess 43 in mold bottom section 61 of mold 60. This can be donemanually or by machine.

Importantly, as shown in FIG. 9 a, prior to the thermoforming,processing of layup 33 requires that an appropriate amount of themicrocapsules 21 be contained in the finished tube 10. Preferably aninterlayer film or core sleeve 40 is positioned between the first fiberlayer in layup 33 and microcapsules 21. Core sleeve 40 functions toeffectively prevent the microcapsules 21, after being expanded by theapplication of heat to form foam plastic 30 (FIG. 9 b), from leakingduring heating of the mold and solidification of the fiber. It alsomaintains the air pressure and prevents overflow which could affect thequality of the finished product. A preferred embodiment of the inventionuses EXPAN-CELL-152 A, a micro encapsulated foaming plastic, which isprocessed at a moderate temperature. It is also believed that obtaininga substantially uniform distribution of the EXPAN-CELL-152 throughoutthe length of the tube by, for example, rolling and tilting the tubewill achieve superior results.

As noted above, layup 33 may be made of flat planar graphite compositematerial and may be closed. This may be done by twisting and knottingthe end of core sleeve 40, or by simply folding and compressing the endsof the tube mechanically. Alternatively a mechanical device like a smallclip may be used. The clip is made of material, for example plasticincorporating graphite fiber, which melts and becomes part of the finalracquet. Alternatively, adhesive may be used in a relatively smallamount, such as plastic which has been softened into a dope through theuse of a solvent, for example acetone. If desired the dope may be formedusing a material which dissolves the plastic of which the dope is made,but which does not dissolve the thermoplastic/graphite fiber composite.Still yet another alternative is to use a solvent for the thermoplasticmaterial in which the graphite fiber may be contained.

There are a number of methods to dispense the microcapsules in thefinished filled fiber tube 10. For example, clear plastic tubes withmicrocapsules inside are premade and then pulled into the layup.Alternatively, the pre-filled tubes may be wrapped by the fiber to formthe finished fiber tube 10. A second method is to pour, inject, ordispose the microcapsules into the fiber tube after they are rolledusing an auxiliary rod or mandrel which can be slid out of the fibertube. Third, fiber tubes containing microcapsules using these methodscan be used to create second and third filled tubes within tubes, withintubes, and so on.

The mold is heated over time where the mold temperature cures the carbonfibers solidifying at a temperature of 130 degrees C. The curing time isoptimally between 20 minutes and 35 minutes. The microcapsules 21 do notexpand to form foam plastic 30 until the heat is stabilized at the sametemperature as that needed to solidify the fibers with the resin. Itscuring in the heating process, as shown in FIGS. 9 a-b, results in thethermal expansion of the microcapsules, creating the internal pressurefrom inside the fiber tube to bulge against the mold cavity wall.Generally, the instructions of the manufacturer of the microcapsulesshould be observed.

In accordance with the invention, when the microcapsules are heated tothe proper temperature, they begin to expand because the shells of themicrocapsules become plastic. The microcapsules forming the core plasticcontinue to expand resulting in their applying pressure to core sleeve40 which, in turn, applies pressure to the graphite material. At thesame time, the heat that was applied to the mold and thus applied to themicrocapsules, is also heating the graphite/polymeric resin sheets whichare also caused to cure. As the microcapsules expand, they may stretchthe sleeve 40 and carbon fiber polymeric sheet tube to the point whereit is driven against the inner walls of the mold, forcing it into theshape of the mold, and also forcing the layers of carbon fiber materialagainst each other. Because the plastic is cured, the layers fuse toeach other and the multiple layers become a single thick structure.

FIGS. 10 and 11 show a second embodiment, where fiber tubes are placedwithin microencapsulated filled tubes and heated to solidify themultiple tubes for additional strength and rigidity in the racquet.

It is noted that the formation of two tubes, the filling of the tubes 12and 12′ with foam plastic and microencapsulated foaming agent and thewrapping of the two tubes with a third tube 16 may be done prior to theapplication of heat to cause the plastic to foam.

Alternatively, microencapsulated foam material may be included in twodifferent forms to form the foam plastic. The individual tubes beingformed as described above (optionally over first and second tubularsleeves), the resultant handle of the tennis racquet is wrapped with asecond layer 16 of thermoplastic carbon fiber sheeting as describedabove (optionally over a third tubular sleeve), and then the assemblyheated a second time to a lower temperature. At the high temperature ofthe first racquet formation step, microcapsules designed to foam at thathigh temperature are used. The other microcapsules foam at the lowertemperature thus allowing a second application of heat and pressure inthe formation of the tennis racquet.

It is also noted that it is possible to form the entire tennis racquetwith double tubes, thus resulting in an internal structure formed of twotubes, generally having a closed form, for example, with a planar walldividing it in half and giving it particular strengths.

In accordance with the invention, it is contemplated that the planarwall may be perpendicular to the plane of the racquet, as illustrated inFIG. 11. However, the planar wall may be parallel to the plane of theracquet, depending upon the playing characteristics which one desires.In connection with this, it is noted that the invention may be used inconnection with products other than sports racquets, such as bicycles,where different configurations of the divider wall which extends alongthe length of the tube may be desired for different parts of thebicycle. In still other items of sports equipment, for example baseballbats, it may be useful to have multiple divider walls extending bothperpendicular to each other, and this may be achieved using fourindividual tubular sections.

In accordance with the invention, it may also be desirable to includemore than four layups in a single structural member.

Still another alternative is for a tube, which wraps two other tubes, tobe filled with the other two tubes and to have plastic andmicroencapsulated foaming agent positioned between the outsides of thetwo inner tubes and the inside wall of the outer tube, and for theentire assembly to be heated to cause the microcapsules to foam andcause the formation of pressure and foam plastic. In accordance withthis alternative, the microcapsules filled with foaming agent, which areplaced between the outsides of the already formed two inner tubes andthe insides of the overwrapping outer tube, are such that foaming iscaused to occur at a lower temperature, and the material which forms thefoam becoming plastic at a lower temperature, so that the heat is neverhigh enough to remelt the plastic formed during the first part of themanufacturing operation.

Finally, the foaming may be done for both the foam inside the twosmaller tubes and the foam inside the overwrapping tube at the sametime.

Fiber tubes 12 and 12′ may be rolled manually or by machine. Thenanother filled fiber tube 16 is created. Finally, the microcapsules aredisposed into both fiber tubes, so as to have a tube within a tube orcomplete a group of tubes in the prefabrication process. This auxiliarytube system allows for the formation of multiple walls within one outertube.

The implementation of such a two step process or group of fiber tubesmay substantially increase strength and performance of many finishedproducts due to additional support within the finished graphitecomposite part.

It should be understood that such multiple tubes are but one optionalexample of the invention. It is to be understood that invention may alsobe embodied in single tube structures, or hybrid structures withmultiple and single tube portions such as the tennis racquet of theabove example. Moreover, multiple tube and or hybrid structures may beof particular importance in relatively high demand applications, such asbicycle frames, automobile body parts and the like. More particularly,in accordance with the invention it is contemplated that graphite fibercomposite members may be made, not only in a two-dimensionalconfigurations, such as tennis racquets and bicycle frames, but also inconfigurations where the axes of the constituent elements extend inthree dimensions, for example a chair, an automobile cabin, or a lawntractor frame.

As is apparent from the above, the multiple tube process also allows thefurther formation of a wide variety of shapes, even without the use ofmolds because they premade outer tube, for example, they graphite fibercomposite tube, which may or may not be made using a mold, acts as acavity wall in lieu of the mold. It can be processed using conveyorbelts to carry it into a furnace to heat cure rather than using molds.This may result in a higher manufacturing efficiency and loweroperational costs. In connection with this embodiment, it is understoodthat the initial set of the tubes or other mold forms into which thelayup is introduced need not be as strong as a conventional iron mold,but merely strong enough to contain the pressure necessary to result inwell formed high-strength graphite composite in accordance with thepresent invention. This embodiment can also be produced solely bymachines with minimal or no human labor.

FIG. 12 a shows a mold 40 into which the handle portion 41 of a racquet10 a is placed for further curing, through the formation of a secondhandle reinforcement member 30 within void space 11 defined by frame 20.

FIG. 12 b shows in cross section another example of a tube 30 structurewithin a tube 20.

FIG. 13 shows an example of a mold 60 defining a cavity 21 for making ahead 18 separately for use in a second molding into a frame.

FIG. 14 illustrates the construction of a badminton racket including ahead portion 10, foam plastic pressurizing material 30, and T-shapedsupport member 72 for receiving the ends 73 of head portion 10. Centralsupport member 71, of T-shaped support member 72, is received within ahandle member 20. Handle member 20 and head portion 10, including theirends, are defined by carbon fiber layups and are securely disposedaround T-shaped support member 72.

FIGS. 15 and 16 show yet another embodiment of the invention whereracquet weight distribution is required. Racquet weight distributionbalance weights 50 can be added into the layout which becomes the fibercomposite tube 10 prior to the solidification and curing process thatattends the application of heat to microcapsules 30. This would bedifficult or impossible with conventional air injection technologybecause the weights might block the coupling of pressure to parts of theracquet. The weights can be made from a variety of materials includingrubber, silicone, plastic, metal or any other materials and substances.

In accordance with the invention, the amount of foaming plastic materialis selected so that it will fill the desired volume and provide thedesired degree of pressure. Other factors are the amount of weight whichthe foam will contribute to the structure, and the structuralcharacteristic of the overall part after the foam core has been formed.Multiple tubes may have substantially equal volumes, assuming thatheating, mold volume and the amount of foam plastic microcapsulesintroduced is uniform. As the mold cavity is uniformly heated, the moldcan be expected to heat the layup uniformly.

The necessity of weights and balances in racquets are well known in theindustry. Conventionally, however, these weights could only be addedafter the solidification of the graphite fiber composite. The thirdembodiment allows weights to be added in the racquet head itself duringthe manufacturing process, for example by placement within sleeve 40(FIG. 6), or placement within the mold cavity. Alternatively, during themanufacturing process, be incorporated for the receipt of weights. Theadvantage of doing this during the manufacturing process is theconsistency and ease with which structural weight can be added duringmass machine production to, for example, balance the racquet head, andthe ease with which the same may be customized after production.

This embodiment also allows the formation of multiple structuresimpossible with conventional technology because air would not be able topass through objects within the tube.

FIG. 17 shows a finished customizable racquet 14 in exploded plan view,including handle portion 15, headweights strip 25 a and 25 b, which canhold weights, handle portion 14 a, and handle weights 16 a, 16 b, and 16c. Alternative handle portions 14 b, and 14 c are illustrated. Handleweights 16 a, 16 b, and 16 c may be 2 g, 5 g, and 10 g, respectively.Buttcaps 5 b and 5 c are customizable and interchangeable.

Racquet 12, with interchangeable handles in different shapes and sizes14, different weights 16, different buttcap designs 5 and differentheadweights 25, allows the user to create the desired weight and balanceand customization points with precision.

The main concept of the method of the present invention is primarily touse the force of the foaming plastic, for example a microencapsulatedfoaming plastic, such as Expancell 152, to create high-pressure insidethe fiber tubes of the layup to form the layup into a thermally curedshape conforming to the mold cavity wall, replacing the traditionalmethod of using compressed air. The system of the invention has numerousadvantages. First, the production method of this invention with theheat-curing and foaming processes in one step, simplify the productionprocess, thus greatly enhancing the efficiency of manufacturingoperations.

Second, the production method of the present invention, the employmentof the pressure of foaming plastic such as is produced by themicrocapsules avoids the air leaks and imprecise manufacturingparameters when using forced air. This has the effect of thereforereducing the manufacturing defect rate.

Third, the method of the present invention also provides for thepossibility of weights installed to provide a completely newinstallation method, which does not require drilling, and can beequipped with weights directly to the internal frame mounted on, forexample, that head.

The present invention allows the more fully automated manufacture ofracquets because there is no air pipe that must be fitted by hand. Theinvention comprises a series of manufacturing steps, none of whichrequires human labor, including a) filling a sleeve with microcapsules,b) saturating the graphite fiber with resin, c) rolling the graphitearound the sleeve, d) bending the graphite fiber lay up into the desiredshape, e) putting the bent layup into a mould, f) heating the mould, g)cooling the mould, and h) opening the mold and taking out the finishedracquet frame.

In accordance with the invention, one may optionally form the holes forthe string during the molding of the racquet frame. The holes may beobtained by forming them on the head of the racquet. Alternatively, apair of layup halves may be used to form the head portion of the racquetframe, and the holes may be formed between the halves by metal postswhich extend across the mold cavity and are supported in slots providedin one or both mold halves.

Turning next to FIG. 18, the manufacture, in accordance with theinvention, of a graphite composite member, for example a sports racquetframe, such as a badminton racquet frame, may be seen in greater detail.More particularly, a sports racquet may be manufactured by firstmanufacturing graphite fabric using Toray's Torayca brand graphite fiberwhich comes in a number of different varieties. It is believed thatTorayca T1000GB, which incorporates 12,000 graphite filaments in a flatribbon of axially aligned fibers, is preferable for a tennis orbadminton racquet frame because of the stiffness of the frame createdusing this material. However, one may also use Torayca T700SC if a moreflexible characteristic in the finished racquet is desired. In the caseof both of these products, the graphite takes the form of a ribbon whichmay be pulled apart transversely to reveal the thousands of fibers whichhave been brought together in the form of a ribbon to enable the facilehandling thereof by processing machinery, such as in the processdescribed below.

Graphite fiber ribbon 100, which comprises Torayca T1000GB, is unwoundfrom a spool 102 and directed by rotatably mounted bar 104 into a vat106. Vat 106 contains a quantity of liquid resin 108. Upon theapplication of sufficient heat, resin 108 is of the type which willharden and cure. In accordance with the preferred embodiment of theinvention, liquid resin 108 is a heat cured epoxy resin sold undercatalog number WH-2370 A by the Wah Hong Industrial Corporation of KaohSiung, Taiwan. Fiber ribbon 100 is diverted into liquid resin 108 by arotatably mounted bar 110. The passage of ribbon 100 through liquidresin 108 is done at the rate of about one to two meters per second andresults in the liquid resin permeating the spaces between the fiberswhich make up graphite fiber ribbon 100.

The permeated ribbon is then fed around the rotatably mounted bar 112.Permeated ribbon 114 is then wound over a release paper layer 116secured to the surface of a rotatably mounted drum 118. In accordancewith the preferred embodiment, ribbon 114 wound on drum 118 to formcoils 120 which slightly overlap each other.

As in the case of prior art tennis racquet manufacturer, the graphitefibers which comprise the racquet are oriented in varying directions.Accordingly, the coils 120 which take a generally cylindricalconfiguration may be cut at different angles, for example along a lineperpendicular to a tangent which is oriented perpendicular to the axisof drum 118. The cutting along such a line may be facilitated by agroove on the drum oriented in the proper direction, as discussed above,with a groove configured to receive the tip of a blade for cutting thegraphite fiber. The various angles are selected to enable the facileassembly of multiple layers of the planar material formed by coils 120.For example, if it were desired to make a three ply graphite planarmember for use in the assembly of a layup, with one layer of fibersoriented horizontally and the other two layers of fibers oriented at±19°, a second groove suitably oriented on the outside surface of drum118 may be used to facilitate cutting of the fibers with the desired 19°orientation.

In order to make a two ply graphite fiber planar member with each plyhaving a different orientation, it is merely necessary to take onegraphite planar member, manufactured using the above process, with itsbacking sheet 116 and exposed graphite fiber layer 120, and place itover the exposed graphite fiber resting on another release member at thesuitable orientation. Working with the graphite permeated with resin andsupported on a single release sheet and then removing the release sheetis preferred for ease of handling. Of course, two planar graphitemembers with the same orientation may be placed at the desired anglewith respect to each other and cut as desired. If a three ply layer isdesired, one of the backing sheets 116 may be removed and anothergraphite planar member positioned over the two ply assembly with theexposed graphite fiber layer 120 in contact with the graphite fiberlayer 120 of the assembly.

It is noted that it is standard practice in the manufacture of graphiteracquets to orient multiple layers in different directions to givestrength to the finished frame structure. The invention may be appliedto any prior art graphite assembly structure, retaining theorientations, lengths, widths, and so forth to achieve a racquet withsuperior playing characteristics. However, the technology and processesof the invention also enable the fabricator to reduce the cross-section,thus limiting the effect of wind resistance and lightning the racquet.The width of the elements forming the hoop of the racquet frame may benarrowed to result in between 2 mm and 5 mm less thickness and/or widthin the cross-section of the hoop portion of the frame (in the case of atennis racquet), while still retaining sufficient strength to string theracquet at high tension.

A multilayer graphite fiber construction 122 is illustrated in FIG. 19.If desired, it can be oriented as illustrated in FIG. 20 to cut a strip124, as illustrated in FIG. 21. Likewise, the fibers may be oriented ata relatively acute angle to each other as illustrated in FIG. 22,allowing the fabrication of a strip from such material as illustrated inFIG. 23.

A badminton racquet may be constructed in accordance with the inventionusing the process described below. Generally, the size and fiberorientation of the various strips of graphite fabric permeated withresin which are used in accordance with the invention to manufacture agraphite composite frame, are the same as those used in the manufactureof a conventional graphite frame, except that the width of the same maybe reduced, because the thickness of the racquet measured vertical tothe plane of the head of the racquet, may be reduced by, for example,two or three millimeters, while obtaining at least sufficient strength.It is also possible in accordance with the invention to reduce thethickness of the frame in the direction of the plane of the head, andsuch expedient will have the effect of reducing wind resistance to themovement of the racquet.

A strip 126 of multilayer graphite material permeated with resin andhaving dimensions of 29 cm×6 cm is illustrated in FIG. 24. The length of29 cm is selected as substantially matching the circumference of thehead of the badminton racquet being manufactured. As illustratedschematically in FIG. 25, strip 126 comprises layers which are at ±19°with respect to the length of strip 126. As illustrated in FIG. 26, asecond strip 127, substantially identical to strip 126 is placed overstrip 126. Following this a narrow strip 128, with graphite fibersoriented perpendicular to the length of the strip, is placed over thetwo strips, with the upper lengths of strips 126-128 all aligned,substantially as illustrated in FIG. 26. A keystone shaped piece 130comprising, for example, two layers with orientations of plus and minus30° is then added to give added strength and provide for the possibilityof putting the strings under high tension. Generally, the assembly 132of strips 126-130 will somewhat stick together because the resin isrelatively tacky, even in its uncured state, thus making handling of theassembly relatively easy.

In accordance with a preferred embodiment of the invention, winding isperformed using a two-part mandrel comprising mandrel parts 134 and 136.Mandrel parts 134 and 136 are placed in a tubular nylon sleeve 138, asillustrated in FIG. 28. Sleeve 138 has a characteristic of not meltingunder the application of heat. Accordingly, it is somewhat oversized, asillustrated in phantom lines in FIG. 29, when it is placed over mandrelparts 134 and 136. As illustrated in solid lines in FIG. 29, the excessportions of the sleeve are folded over themselves and over a length ofdouble stick tape 140 in order to snugly and securely contain themandrel parts. The excess portions of the sleeve also act to accommodateexpansion of the sleeve as it pushes against the layers of graphitefiber permeated with resin. During this process, layers of resin mayslide with respect to each other.

Mandrel parts 134 and 136 have a width of about 8 mm and a thickness ofapproximately 1.5 mm and may be made of, for example, steel. The mandrelis provided in two mandrel parts 134 and 136 in order to provide forremoval of the mandrel from the layup without difficulty and whileminimally disturbing the rolled layup, as more fully appears below.

Assembly 132 is then wrapped around the nylon sleeve 138 on mandrelparts 134 and 136, for example by rolling, as illustrated in FIG. 30.Rolling is continued as illustrated in FIG. 31. Before rolling has beencompleted, a pair of end strips 142 (constructed of fibers in a numberof layers oriented at angles with respect to their length typical of theprior art) illustrated in FIG. 32 and a length strip 144 (of prior artlength, width, fiber orientation and number of layers), as illustratedin FIG. 33 are positioned on the assembly 132, as illustrated in FIG.34. Rolling is then continued until all the graphite layers have beenrolled around the mandrel, as illustrated in FIG. 35. End strips 142might have their graphite fibers oriented parallel to their length,while length strip 144 may comprised of graphite fibers orientedperpendicular to the length of the strip. The length, width, fiberorientation and number of layers of fibers are known in the prior artand form no part of the invention.

Following this, additional layers of graphite strips are wrapped tocomplete the layup. More particularly, another pair of end strips, forexample, identical in orientation and size to end strips 142, andanother length strip identical to strip 144 are positioned over theassembly illustrated in FIG. 35. Following that, a final wrapping sheetof two ply graphite fabric with fiber orientations at plus and minus 30°and having a width of approximately 4.5 to 7 cm is wrapped over theassembly illustrated in FIG. 35 to result in the assembly illustrated inFIG. 36.

When the layup is completed as illustrated in FIG. 36, mandrel part 134is removed from the layup by the pulling of the same from the layupwhile the opposite end of nylon sleeve 138 is grasped by the other hand.With opposite motions, mandrel part 136 is removed from the layupleaving the inside of sleeve 138 open.

One gram of Expancell 152, which is designated by reference numeral 146,is then placed in the half cylindrical spoon portion 148 of spoon 150(FIG. 37). Foam plastic forming material 146 is spread more or lessevenly the entire length of spoon portion 148. Spoon portion 148 has alength which is approximately equal to half of the length of nylonsleeve 138. Spoon portion 148 is then inserted into layup 152 (FIG. 36).Spoon 150 is then rotated axially, releasing and substantially uniformlydistributing foam plastic forming material 146 along one half of layup152. The process is then repeated using another gram of Expancell 152 tofill the other half of layup 152.

The ends of nylon sleeve 138 are then tied closed and the layup rotatedand rolled by hand to further even out the distribution of foam plasticforming material 146. Layup 152 is then wrapped around a wooden mold 154(FIG. 38) to form it generally in the shape of a badminton racquetframe. Referring to FIG. 39, a tubular member 156, which may be graphitecomposite or some other material, is then cut to form a slot 158 forreceiving a crosspiece 160, which may be glued in position asillustrated. The parts are then arranged as shown in FIG. 40.

The ends of layup 152 are then pushed in the direction of arrows 162over the ends of crosspiece 160, as illustrated in FIG. 41. Strips 164,166 and 168, each of which may be 10 cm long and 1.5 cm in width, arethen positioned as illustrated in FIG. 41, being pressed against theframe members to serve the function of binding them together inposition. Strips 164, 166 and 168 may all be two ply graphite memberswith one layer aligned at +45° with respect to its length and the otherlayer aligned at −45° with respect to the length of the strip.

As is schematically illustrated in FIGS. 42-49, additional strips170-184 are next applied to the layup for the badminton frame.

Strip 170 is applied in a u-shape as illustrated in FIG. 42. Strip 172is wrapped around the head starting on the left side and wrapping aroundthrough the center and onto the right side of the head. Strip 174 iscoiled around the handle of the racquet frame. Strip 176 is barbellshaped. Strip 176 is centered on the junction between the handle and thehead or hoop and is then spirally wrapped tightly around both sides ofthe adjoining oval-shaped head portions. Referring to FIG. 46, elongateddiamond shaped patch 178 is passed through the head, centered on thehandle and both ends of the patch 178 are wrapped around and broughtinto contact with the handle, wrapping around its sides. An elongatedparallelogram shaped patch 180 is then placed over diamond shaped patch178, and pressed against the handle and other parts of the racquet.

Generally, it is noted that all wrapping of resin-permeated graphitefiber patches is done tightly and in close conformity to the alreadyassembled portions of the frame structure. The stickiness of the resinsaturating the graphite fiber patches facilitates this. As shown in FIG.48, a second parallelogram patch 182 is positioned over the firstparallelogram patch 180. As shown in FIG. 49, patches 184 and 186 arethen adhered to the outside half-arch shaped portions of the racquet.

As shown in FIG. 50, the badminton racquet frame layup is placed in thecavity 188 of mold bottom 190. The mating top of the mold is then placedover mold bottom 190. Care should be taken not to pinch the graphitefibers. This is done by ensuring that the layup is contained in andpositioned over cavity 188. The assembly is then heated to cure theresin. Heating may be done by putting the mold in an oven, or bycirculating a hot liquid, such as water or oil, within passages providedin the mold for this purpose. In order to cure the graphite/resinmembers forming the layup, the layup should be heated to about 145° C.with a tolerance of plus or minus 5° C. However, this temperaturedepends upon the particular foam plastic forming material being used andany temperature, which achieves foaming, curing and expansion of theplastic, and sufficient pressure, is likely to result in the productionof an excellent frame.

Heating should continue for about 25 minutes, although longer heatingtimes do not appear to adversely affect the final product. Theapplication of heat results in pressure being exerted against thegraphite layers of the layup, forcing them against each other to form astrong structure and, perhaps, some shifting with respect to otherlayers during this process.

Once heating has been completed, it is best that the mold be cooled, forexample by circulating cold water in the passages provided in the moldfor the purpose of heating and cooling the mold. This is necessary sothat the foam plastic formed by the Expancell 152 will solidify well,thus preventing, potentially, further expansion of the frame materialupon removal of the racquet frame from the mold. Cooling to 10-15° C.has been found to result in the production of frames with excellentcharacteristics, although it is not believed that this particulartemperature range is very critical. The racquet is then ready to beprocessed in a conventional manner by finishing, drilling holes,stringing and the application of an appropriate handle grip.

While, in principle, the mating mold halves may have passages forheating and cooling, it is also possible for a mold without suchpassages to be placed between a pair of metal plates with such passages,which may be used to receive hot and cold fluids for heating and coolinga two-part clamshell mold securely held between the metal plates.

The manufacture of a tennis racquet will now be described. The frame ismade, as above, using a nylon tube snuggly secured around a mandrelusing double stick tape. The process steps for making a tennis racquetframe are similar to those employed in the making of a badmintonracquet, except that the amount of carbon fabric and foam plastic issubstantially larger.

In accordance with the inventive fabrication of a tennis racquet using anumber of graphite fabric strips, which are illustrated in FIG. 51, thelayup 210, when formed into a racquet extends from the base of thehandle of the racquet through the length of the handle, around thecircumference of the head of the racquet and back along the length ofthe handle to the base of the handle of the racquet, as illustrated inFIG. 52. A throat is formed by a crosspiece 212 which completes thecircumference of the head of the racquet. Crosspiece 212 may be madeusing the inventive process, although its characteristics are not at allcritical because it is well supported and is short in length. Crosspiece212 may be supported by spirally wound, sideways positioned, or otherstrips of graphite-resin fabric, as in the case of the badminton racquetmanufacturing process described above. After the layup is formed it isput in the general shape of a tennis racquet my being formed around awooden mold. Crosspiece 212 is then added and secured with strips ofcarbon fiber permeated with resin as described above. The fiberstructure can then be completed by wrapping of the handle with severallayers of graphite fiber with different orientations to give strength inall directions.

Referring to FIG. 51, a schematic exploded plan view of the primaryparts of a tennis frame is illustrated. FIG. 51 does not show the partsof the crosspiece which define the throat of the tennis racquet frame,but the construction of the crosspiece will be described after thedescription of the construction of FIG. 51. It is noted that in thisexploded view, parts which are identical have only been illustrated oncein some cases as will be understood from the following.

After the sleeve has been wound and secured around the twin mandrels, afirst strip 216 having a length of 155 cm is centered on the nylonsleeve and wound snugly thereon. Strip 216 comprises two layers ofgraphite fibers oriented at +30° and −30° with respect to the length.The strip has a width of 7.2 cm. The various strips of graphite/resinmaterial are set forth below in the order in which they are wrapped overthe nylon sleeve covering the mandrel. Next, strips 218 and 220 arepositioned 74 cm from the centerline 222 of the layup. Strips 218 and220 are trapezoidal in shape and have two layers of graphite fibers, oneof them +30° with respect to the length and the other −30° with respectto the length of the strips. After strips 218 and 220 are applied, asecond pair of strips identical to strips 218 and 220 (which have awidth of 7.2 cm, and a long length of 11 cm and a short length of 9 cm)are next applied. Optionally, they may be positioned with oppositeorientations up and down as illustrated. These strips are laid down overwhat will be the outside of the frame.

FIG. 51 may be understood as showing the distances of the various endsof the carbon fiber strips from the centerline 222 of the layup. Thus,strip 216 is centered on the layup, has a length of 155 cm and has endswhich are each 77.5 cm from centerline 222. Similarly, strip 218 has along length of 11 cm, a short length of 9 cm, and is positioned at adistance of 74 cm from centerline 222. The positions of the various endsand corners of the strips in centimeters from the centerline of thelayup are given in FIG. 51.

Strip 224 is trapezoidal in shape and extends from a point 82 cm fromcenterline 222 (on the left) to a point 5 cm from centerline 222 (on theright). Strip 226 is a mirror image of strip 224. Strip 226 istrapezoidal in shape and extends from a point 82 cm from centerline 222(on the right) to a point 5 cm from centerline 222 (on the left). Strips224 and 226 are 87 cm long and have two ply graphite fiber strips withthe layers extending at +10° and −10° with respect to the length of thestrip. After strips 224 and 226 are applied, an identical pair of stripsare applied over them.

Strip 228, which has a length of 130 cm is also a two-ply graphite fiberconstruction with layers at +30° and −30° with respect to their length.Such a strip is also applied twice, optionally positioned upside downfrom top to bottom during the second application. Unlike strips 216-226,strips 228 are applied to what becomes the inside of the racquet frame.Strips 224, 226, and 228 all have a width of 7.2 cm.

Strip 230, which has a length of 92 cm and a width of 2 cm, is appliedto the outside of the racquet head and comprises fibers which aretransverse to the length of strip 230. It is noted that when thegraphite fiber fabric strips are applied, they are handled while theyare still on the release paper (as is preferably the case with allgraphite fiber strips used in the method of the present invention). Thisis particularly important in the case of strip 230. After they areapplied to the layup, the release paper is pulled off.

Strip 232, which has a width of 0.5 cm, has two layers with fibersparallel to its length. It is wrapped on the outside of the racquetlayup. Strip 232 is applied to that portion of the layup which becomesthe face of the racquet. A second strip identical to strip 232 isapplied to what becomes the opposite face of the racquet.

Strip 234, which has a width of 2 cm, has a length of 12 cm andcomprises two layers of graphite fibers, one of the layers having fibersparallel to the length of the strip and the other having fibersperpendicular to the length of the strip. After a first strip 234 isapplied to the inside of the layup, a second identical strip 234 isapplied to the outside of the layup.

Strips 236 have a width of 3 cm and are two layer constructions withgraphite oriented at +10° and −10° with respect to the length of thestrips. After a first set of strips 236 have been applied to the outsideof the layup, a second set of strips 236 are applied to the inside ofthe layup.

Strip 238 has a width of 2 cm and a length of 90 cm and is applied tothe inside of the layup. Strip 240 has a width of 7.5 cm and is appliedto the inside of the layup. Strip 240 is a two layer structure withlayers oriented at +30° and −30° with respect to its length. Two strips240 are applied to the inside of the layup.

Strip 242 has a width of 7.9 cm and a length of 122 cm, and is comprisedof two layers with fibers oriented at +10° and −10° with respect to thelength of strip 242. Two such strips 242 are applied to the outside ofthe layup.

Strip 244 has a length of 155 cm and a width of 8 cm, and is a two layerconstruction with graphite fibers oriented at +30° in −30° with respectto the length of strip 244. Two such strips 244 are applied to theoutside of the layup.

Each strip 246 has a width of 7.5 cm and a length of 11 cm. The strips246 are two layer structures with fibers oriented at +30° and −30° withrespect to the length of the strips. Four such pairs of strips 246 arewrapped around the outside of the layup.

Strip 248 has a width of 2 cm and a length of 10 cm, and comprises a twoply structure with fiber orientations at +10° and −10°. Two such strips248 are applied to the inside of the layup. As with other trapezoidaland parallelogram shaped strips, positions may be reversed from top tobottom, as illustrated, with the second set of strips to achievesymmetry in the structure. Two such strips 248 are used.

Strip 250 has a width of 3 cm, and comprises a four ply structure, withgraphite layers oriented at +10°, −10°, +30°, and −30°.

In connection with the above, it is again noted that any structure builtusing the conventional air pressure system using an external airpressure source may be used identically or adapted to the reduction inthe amount of material needed and used to implement the inventivemethod.

After the main portion of the frame layup is completed using the stripsillustrated in FIG. 51, 25 g of Expancell 152 is loaded in the nylonsleeve on which the graphite/resin strips are wrapped. This is done intwo doses, each of 12.5 g which are inserted in each half of the layupcorresponding to the mandrel on which the layup was wrapped. Followingthe introduction of Expancell 152, the ends of the nylon sleeve areknotted or otherwise closed to ensure that pressure will be maintainedduring foaming of the plastic core.

A layup for crosspiece 212 is then constructed by wrapping on a mandrelcovered by a tubular nylon member snuggly secured thereto by doublestick tape, for example ordinary double stick tape of the sort used inoffice clerical applications. As in the example of a badminton racquetabove, the various strips of graphite/resin material are set forth belowin the order in which they are wrapped over the nylon sleeve coveringthe two mandrels.

The first strip measuring 6 centimeters in width and 12 cm in length isfirst wrapped over the nylon sleeve. Its fibers are oriented at +30° andat −30° with respect to the length of the strip. The strip is followedby another strip with fibers oriented at +10° and −10° with respect tothe length of the strip, and having a length of 11 cm and a width of 11cm. Next a strip with fibers oriented at +30° and −30° with respect tothe length, and having a length of 21 cm, a width of 11 cm and havingits ends tapered over a distance of approximately 2.5 cm is wrappedaround the prior layers.

Another strip, having a length of 10 cm and a width of 2 cm, alsocomprising two layers, but with fiber orientations at +10° and −10° withrespect to the length of the strip, is then added to the assemblage.This strip is wrapped over what becomes the inside of the head of theracquet.

Another strip, having a length of 10 cm and a width of 2 cm, alsocomprising two layers but with fiber orientations at 90° and 0° withrespect to the length of the strip is then added to the assemblage. Thisstrip is centered and wrapped over what becomes the outside of the headof the racquet.

Next a strip with fibers oriented at +30° and −30° with respect to thelength, and having a length of 21 cm, a width of 4.5 cm and having itsends tapered over a distance of approximately 2 cm is wrapped around theprior layers. After this, a strip with fibers oriented at +30° in −30°with respect to the length, and having a length of 10 cm and a width of7 cm, is wrapped around the prior layers.

After the layup for crosspiece 212 has thus been formed and the mandrelremoved, 2 g of Expancell 152 are introduced into the nylon sleeve uponwhich the layup for crosspiece 212 has been wrapped. The ends of thenylon sleeve are then knotted closed, preferably with knots positionedin the tube defined by the graphite layers of the crosspiece layup. Thiscompletes the construction of the crosspiece layup. Optionally, one mayomit the step of knotting the ends of the nylon sleeve on the crosspiecelayup, as the mold and pressure from adjoining portions of the headportion of the main layup will exert pressure (due to expansion of thefoam) and seal the ends of the crosspiece layup during heating andcuring.

As shown in FIG. 52, layup 214 comprises crosspiece 212 and mainframeportion 210. The same are put into the desired shape using a wooden formas illustrated FIG. 53 before receiving additional strips and patches ofresin permeated fiberglass, and being put in an iron mold bottom member216, as illustrated in FIG. 54. The wooden form comprises a head support218 and a throat support 220. After this, additional strips and patchesare added to the layup as will be described below. After this, thefinished layup may be placed in the iron mold bottom member 216, asshown in FIG. 54.

Referring to FIG. 55, the knotted ends of the nylon sleeve, with knots218 may extend from the iron mold. Alternatively, as illustrated in FIG.56, knots 222 may be tucked in between the filled layup, and the moldmay be configured to form a flat bottom, thus eliminating the need forsawing at the base of the handle as in the embodiment of FIG. 55.

Referring to FIG. 57, the process for attaching crosspiece 212, bywrapping the additional strips and patches referred to above, may bebetter understood.

More particularly, as illustrated in FIG. 57, crosspiece layup 224receives a second tubular graphite/resin support member. This secondtubular graphite/resin member is constructed by rolling into a tube atwo layer graphite strip permeated with resin, having a length of 10 cmand a width of 21 cm with tapered ends, and having its layers orientedat +30° and −30° with respect to the length the strip. The tube shouldhave a diameter such that when the support member 226 is flattened, ithas a width which is a little less than the thickness of the finishedracquet frame.

This second tubular graphite/resin member is constructed by rolling intoa tube a two layer graphite strip permeated with resin, having a lengthof 10 cm and a width of 7 cm, and having its layers oriented at +30° in−30° with respect to the length the strip. The tube should have thediameter such that when the support member 226 is flattened, it has awidth which is a little less than the thickness of the finished racquetframe.

Another graphite/resin strip 228 is rolled around the combination ofcrosspiece layup 224 and support member 226. Strip 228 is a two layergraphite strip permeated with resin, having a length of 10 cm and awidth of 7 cm, and having its layers oriented at +30° and −30° withrespect to the length of the strip. The strip 228 is wrapped around thecentral portion of the combination of crosspiece layup 224 and supportmember 226, as illustrated in FIG. 58.

After crosspiece layup 224 has been constructed, it is positioned on thewood form of FIG. 53 together with the main portion 210 of the racquetframe, to which it is to be secured. The ends 230 and 232 of crosspiecelayup 224 and support member 226, respectively, are bent away from eachother as illustrated in FIG. 59. Main portion 210 and the combination ofcrosspiece layup 224 and support member 226 are then put on the woodform of FIG. 53. The relative position of the frame elements may bebetter understood from FIG. 60 which omits the illustration of the woodform for purposes of clarity of illustration. All four ends 230 and 232are then bound by strips of graphite fibers permeated with resin havinga length of about 12 cm and a width of about 1 cm. These may be singleply graphite fiber strips with fibers oriented along the length of thestrip. Binding is done by smoothly spirally winding the same with slightoverlap to the extent possible between the edges of the strip asindicated schematically by the spirals 234 in FIG. 60. While spirals arenot illustrated for the other ends, they are wrapped in the same manner.

The handle portion of the frame is wrapped with two strips of carbonfiber fabric each having a two layer construction with fibers running+30° and −30° with respect to the length of the strip. The strips areboth 17 cm long and 4 cm wide.

The finished layup is then removed from the wooden form and placed inthe bottom half of an iron mold for heating. In the event that aclosed-handle iron mold, such as that illustrated in FIG. 61 is used,one may dispense with knotting the ends of the nylon sleeve forming thelayup for the main portion 210. The ends of the nylon sleeve may simplybe folded over and positioned between the two ends of the main portionof the layup. Such simple folding over may optionally be employed forthe ends of the nylon sleeve of the crosspiece, taking care to tuck theminto the tube formed by the wound graphite layers that make up thecrosspiece.

In accordance with the invention it is also possible for a graphitecomposite member to be manufactured without the use of any impermeablemembers, such as the tubular nylon sleeve. In this case, graphite stripsare wound directly upon a mandrel, perhaps with the first layers ofresin permeated graphite having one side coated with a parting agent,such as an inert powder to prevent them from sticking to the mandrel.The tubular layup may then be built by successive wrapping of additionalgraphite/resin strips. When wrapping of the layup is completed, thefinished layup may have its ends folded over upon themselves tosubstantially seal them and then the part, for example a tennis racket,may be put in a closed mold, such as that illustrated in, for example,FIG. 56. In addition, it is also possible to use an open, for example,half cylindrical mandrel having the configuration of spoon 150, andhaving plastic forming material (for example Expancell 152) in its spoonportion 148 prior to wrapping of the layup. It may be also desirable tomake spoon portion 148 square in cross-section or some other shape. Whenusing such a spoon mandrel, after the layup has been wrapped, the layupneed simply be rotated to allow the plastic forming material to fall onthe inside surface of the layup and then to remove the spoon, and foldover the ends to seal them before placing them in a mold for heating andcuring as shown in FIG. 56.

Turning to FIG. 61, a particularly advantageous embodiment of theinvention is illustrated. In this embodiment, a tennis racket layup 310is made up of two tubular members, namely inner tubular member 312 andouter tubular member 314. Inner tubular member 312 and outer tubularmember 314 are each made substantially in the same manner as the tubularlayups described above, and comprise an inner tubular member filled witha heat activated expandable material such as Expancell and sealed, andcovered with members comprising graphite fiber permeated with athermoplastic or thermal setting material.

As can be seen from FIG. 62, inner tubular member 312 is shorter thanouter tubular member 314 because it merely extends around the head ofthe racquet, starting at end 316 and extending around the head in acounterclockwise direction, ending at end 318 which is positionedadjacent end 316. After being heated in a tennis racket mold, end 316 isjoined and fused to end 318 at juncture 320, as illustrated in FIG. 63.

Optionally, a number of binding strips 322 of graphite fiber permeatedwith thermosetting or thermoplastic resin may be used. A smaller numberof longer binding strips, or a larger number of narrower binding stripsor a combination of the same may be used. For example, twenty-five 1 cmwide strips may be dispersed uniformly throughout the frame.

After tennis racket layup 310 has been completed, it is placed in a mold324 in accordance with the preferred embodiment, as illustrated in FIG.61. In accordance with the invention, as in the previously describedembodiments, the layup is placed in the mold, and the mold is closed andheated causing the powder to expand and drive the graphite and resin tothe inter surfaces of the mold, causing it to take the form of the mold.At the same time, inner tubular member 312 is very securely fused toouter tubular member 314. In this embodiment, it is noted that bridgeportion 326 is, accordingly, very securely fused to the remainingportions of the finished racket. In addition, the structure is moreuniform compared to the earlier described embodiments and thus does nothave discontinuities in its characteristics.

At the same time, the outer tubular member extends from the base of thehandle of the racquet, around the head of the racquet and back to thebase of the handle of the racquet in a single continuous member thusproviding strength to the handle 328 and the handle extensions 330 bywhich the handle is secured to the head 332.

In accordance with the preferred embodiment, those portions of outermember 314 which form part of the head may be made with less materialthan other portions of outer member 314 because they are reinforced byportions of inner member 312. Likewise, those portions of inner member312 which form part of the head may be made with less material thanother portions of inner member 312 because they are reinforced byportions of outer member 314.

In principle, it is also noted that inner tubular layup 312 may befilled with Expancell or other similar foaming plastic and outer tubularlayup 314 may be inflated with air thus giving a hybrid performancecharacteristic in the finished racket frame.

While illustrative embodiments of the invention have been disclosed, itis understood that various modifications of the inventive method and thematerials used will be obvious to those of ordinary skill in the art inview of the above description and specification. In addition to theseobvious modifications, the invention may be applied in other areas. Forexample, the inventive technique may be used to form a bicycle frame inwhich different orientations are applied to different parts of the frameto address the stresses formed at those parts of the frame during use.Such variations are within the spirit and scope of the invention whichis limited and defined only by the appended claims.

1. A resin and fiber composite racket comprising a first tubular memberwhich extends around the head of the racquet and a second tubular memberwhich extends from the base of the handle of the racquet, around thehead of the racquet and back to the base of the handle of the racquet,each of said tubular members comprising: (a) an outer shell defining acavity, said outer shell comprising: (i) a plurality of layers offibers; (ii) a first resinous material disposed between said fibers andsecuring said fibers to each other; (b) a second resinous materialdisposed inside said cavity, said second resinous material beingconfigured and dimensioned to define voids within said cavity betweenportions of said second resinous material; and (c) a gaseous materialcontained within said voids, said gaseous material being under apressure in excess of 30 pounds per square inch.
 2. A resin and fiberracket as in claim 1, wherein said first tubular member is an innertubular member and said second tubular member is an outer tubular memberand those portions of said outer member which form part of the head maybe made with less material than other portions of outer member, andthose portions of said inner member which form part of the head may bemade with less material than other portions of inner member.
 3. A resinand fiber composite racket comprising a first tubular member whichextends around the head of the racquet and a second tubular member whichextends from the base of the handle of the racquet, around the head ofthe racquet and back to the base of the handle of the racquet.
 4. Aracquet as in claim 3, wherein said first and second tubular membersmade from strips of graphite fiber material including a resinouscomponent surrounding an expandable material which expands under heatand are formed by expanding said expandable material and driving saidgraphite fiber material to the edges of said mold.